Manganese dioxide is a known material for use as a cathodic material in batteries. It also is known that it is not particularly suitable for rechargeable batteries. Apparently irreversible structural changes occur in manganese dioxide during discharge which do not permit recharging.
Lithiated manganese oxide made from manganese dioxide (MnO.sub.2) has been investigated for use in rechargeable batteries. The method of making the lithiated manganese oxide and the manganese dioxide starting material appears to materially affect the effectiveness of the lithiated manganese oxide used in rechargeable batteries. U.S. Pat. Nos. 4,312,930 and 4,246,253 to Hunter describe a lithiated manganese oxide which Hunter says has a particularly effective utility for rechargeable batteries. Each of these Hunter patents is incorporated herein as if fully rewritten.
Making lithiated manganese compounds is not necessarily new. Monchilov and Manev describe making lithiated manganese compounds (see Journal of Power Sources, 41 (1993) 305-314 and Log Batteries, Battery Mater., Vol. 14 (1995), respectively), but do not describe making such compounds from relatively impure compounds which have a high sodium and/or potassium content and making relatively pure lithiated manganese compounds by removing the sodium and/or potassium and replacing those alkali metals with lithium to make a pure lithiated manganese compound.
U.S. Pat. No. 5,759,510 to Pillai and copending application Serial No. PCT/US97/17081, filed Sep. 30, 1997, (which is a continuation-in-part application from the application which matured into U.S. Pat. No. 5,759,510) describe making lithiated manganese oxide from manganese dioxide. When compared to the process described herein, the process described in these copending applications are more complex, require higher temperatures, do not use an ion exchange reaction, and hence require more severe conditions in making an initially calcined product which is thereafter calcined. As a result these processes are more likely to generate more impurities and are more energy intensive.
An object of this invention is to provide a process for making lithiated manganese oxide.
Another object of this invention is to use chemically made manganese dioxide having sodium and/or potassium ions in making the lithiated manganese oxide by the process of the invention.
Yet another object of this invention is to make a pure form of lithiated manganese oxide from the reduction of a sodium and/or potassium permanganate or manganate and controlling the ratio of sodium and/or potassium ions in the amorphous manganese oxide which results from the reduction of the permanganate or manganate such that the lithiated manganese oxide has a utility that is particularly effective for a cathodic material for rechargeable batteries.
Yet another object of the invention is to make a lithiated manganese oxide by a process which has few steps, has a low manganese and lithium loss and is energy efficient.
Further objects and advantages of the invention will be found by reference to the following specification.
As used herein, LiMn.sub.2 O.sub.4 means a lithiated manganese oxide with the general formula Li.sub.1+x Mn.sub.2-y O.sub.4 where x is greater than about -0.11 and less than about +0.33, and y is equal to about 0 to about 0.33.
As used herein, "amorphous manganese dioxide" means a manganese dioxide which does not have a substantially identifiable crystal structure as determined by x-ray diffractometry.
As used herein, "delta manganese dioxide" means a manganese dioxide which does not have a single crystal structure which dominates to provide a manganese dioxide with at least one identifiable crystal structure. Delta manganese dioxide is often described as having the following general formula M.sub.2 O.4MnO.sub.2 where M is an alkali metal cation.
As used herein, "reducing permanganate" means taking the oxidation state of manganese (VII) to manganese (III or IV).
As used herein, "substantially all Mn IV" means at least about 90 weight percent Mn IV and not more than about 10 weight percent Mn III.
As used herein, "defect spinel" is all material within the general formula Li.sub.1+x Mn.sub.2-y O.sub.4 where x is greater than about -0.11 and less than about +0.33 and y is about 0 to about 33, but not LiMn.sub.2 O.sub.4 (where x & y are 0). A specific defect spinel which has utility is where the Li to Mn ion molar ratio is about 0.5.
Another type of defect spinel which has utility is a stoichiometric spinel where the oxidation state of the manganese varies from about 3.5 to 4.0. In the former example of a defect spinel, the Li to Mn ion molar ratio is controlled by how much sodium and/or potassium ions are in the MnO.sub.2 and pH control of the reaction (through the use of LiOH) to get the spinel. To raise the Li to Mn ratio to about 0.6, the pH should be raised. The nature of stoichiometric spinel may be controlled by reaction temperature. Increase the reaction temperature to get the spinel and decrease the oxidation state of the Mn.